Class 2 (2nd Engineer) MET 📅 Feb 2024

Exam Question

(a) What are the factors which determine the synchronous speed of a motor? (6)

(b) The star-connected rotor of an induction motor has a stand-still resistance of 4.5 ohms/phase and a resistance of 0.5 ohms/phase. The motor has an induced emf of 50 V between the slip-rings at stand-still on open circuit when connected to its normal supply voltage. Find the current in each phase and the power factor at start when the slip-ring is short-circuited (10)

Reference Answer

(a) The synchronous speed of an AC motor is determined by two primary factors:
Supply Frequency (f)
Number of Poles (P)
The relationship between these factors and the synchronous speed (Ns) is given by the formula:

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